Spinal Cord Neoplasms/diagnosis; Ultrasonography; Adolescent; Adult; Aged; Astrocytoma/diagnosis; Astrocytoma/diagnostic imaging; Astrocytoma/surgery; Child, Preschool; Ependymoma/diagnosis; Ependymoma/diagnostic imaging; Ependymoma/surgery; Female; Humans; Male; Middle Aged; Neoplasm Recurrence, Local; Postoperative Period; Radiography; Spinal Canal/diagnostic imaging; Spinal Canal/pathology; Spinal Canal/surgery; Spinal Cord Diseases/diagnostic imaging; Spinal Cord Diseases/surgery; Spinal Cord Neoplasms/diagnostic imaging; Spinal Cord Neoplasms/surgery; Ultrasonography/methods